1. Field of the Invention
The present invention relates to a device mounting board used to mount semiconductor devices thereon, a semiconductor module and a mobile apparatus.
2. Description of the Related Art
In recent years, with miniaturization and higher performance in electronic devices, demand has been ever greater for further miniaturization and higher density of semiconductor devices used in the electronic devices. In response to such demand, widely known is a semiconductor module stacking technique such as a 3D packaging technique which is called a package-on-package (PoP) where two or more packages are installed on top of one another.
When semiconductor modules are to be stacked together, a method is employed where an electrode pad provided on a substrate of a lower-side semiconductor module is connected to an electrode pad provided on a back side of an upper-side module using bonding members such as solder balls. Known as connection structures using the solder balls are, for example, a structure where solder balls are connected on a flat electrode pad and a structure where solder balls are connected to an electrode pad having a stepped portion. Also known is an electrode structure of non-solder-mask-defined (NSMD) type where there is a clearance between an electrode pad and a solder mask (insulating layer).
In the structure where the bonding members such as solder balls are mounted on the flat electrode pad (electrode portions), the problem of weak joint strength relative to the force acting along a horizontal direction needs to be addressed. In the structure where there is provided a stepped portion in the electrode pad, there is a problem where the stress tends to be concentrated in corners (edges) of the electrode pad and cracks are likely to occur between the solder balls and the electrode pad.
In the conventional electrode structure of NSMD type, the leader lines connected to the electrode pad are exposed. Thus the problem of a likelihood of disconnection of the leader lines with the stress applied thereto needs to be addressed.